Ion exchange methods using a closed loop system have been utilized for a variety of industrial and agricultural processes to remove unwanted anions and cations from solutions. The continuous operation of ion exchange reaction units having moving beds has been taught by I. Higgins in a multitude of patents including U.S. Pat. No. 3,194,663 for the radioactive decontamination of milk, U.S. Pat. No. 3,492,092 for an ion exchange process for treating crude mineral solutions, U.S. Pat. No. 3,579,322 for the recovery of phosphate from phosphate containing pond water, U.S. Pat. No. 3,580,842 for a downflow ion exchange, U.S. Pat. No. 3,677,937 for a split loop contactor, U.S. Pat. No. 3,775,088 for a process for treating fertilizer plant waste streams, U.S. Pat. No. 3,984,313 for a process for removing ammonia and phosphates from sewage water, and U.S. Pat. No. 5,277,822 for the extraction of thermally stable contaminants from stack gas scrubbing amines.
The Higgins system for ion exchange teaches a continuous, countercurrent, exchange column loop system in which removal or recovery of a targeted cation or anion occurs in one section and the regeneration of resin in another. Two or more liquids of differing specific gravity contact particulate solids in a closed system with little or no dilution and intermixing. A continuous ion exchange apparatus performs both ion exchange treatment and regeneration treatment within a single looped column by the use of ion exchange resin whose ion exchange abilities can be regenerated by acid, salt or alkali. The typical Higgins apparatus comprises unshaped closed tube having an adsorption or treatment zone, a washing or rinsing zone, a regenerating zone and in more current versions, a pulsing zone. The zones or sections are separated by valves. After the resin is regenerated, the influent flow of solution to be treated and regeneration flow are interrupted and the ion exchange resin bed is shifted from one section to another contiguous section so that a portion of the resin in the treatment zone is replaced with regenerated resin.
Later continuous ion exchange systems that employ the Higgins Loop™, a trademark of Tetra Process Technologies, a Severn Trent Services Company, incorporate a pulse cycle to hydraulically move the spent resin out to the treatment vessel and move regenerated resin into the vessel. Chopra in U.S. Pat. Nos. 3,972,810, 4,057,494, Removal of Chromium Chromate Molybdate and Zinc utilizes the Higgins Loop™ system.
Kashiwabara et al. in U.S. Pat. No. 3,993,562 uses a loop-style continuous ion exchange unit having a liquid treating section, a material weighing and transfer section, a regeneration section, a washing section and a back-washing section. The back-washing section is above the liquid treating section to enable material to fall by gravity into the liquid treating section. The liquid treating section is located above the material weighing and transfer section so that material can fall by gravity into the material weighing and transfer section.
Iwatsuka, et al., U.S. Pat. No. 5,580,445 discloses a continuous ion exchange apparatus capable of performing both ion exchange treatment and regeneration treatment within a single column by the use of ion exchange resin(s) whose ion exchange abilities can be regenerated by acid or alkali. A resin extraction transfer means is used for withdrawal of the ion exchange resin from the bottom of the column and transferring them to a metering container disposed on the top of the column and a regenerant passage system allowing the supply of the regenerant from the bottom of the regeneration zone into the interior of the column and discharge of regenerant waste from the top of the regeneration zone to the exterior of the column.
None of these references, however, teach or suggest a continuous counter current ion exchange within a closed loop that automatically adjusts resin regeneration and reduces the significant amount of environmental wastes generated by the system. Arion, in U.S. Pat. Nos. 3,956,115 and 4,002,455 discloses a complex process for regeneration of ion exchange resins and recovering waste water from the fertilizer manufacturer. This process requires extensive equipment and at least 24 steps to accomplish.